Valves, such as butterfly valves, are used to control the flow of a substance such as a liquid or a gas. Often, such valves are used to control the flow of fluids which are hazardous for the reasons of toxicity, radiation or corrosion. When used in such hostile environments it is necessary to completely seal the external valve actuator to prevent any leakage of the hazardous fluid. In the past it has been common to use a packing material or other sealing material around the valve stem to prevent leakage. Such materials, with time, will wear and the chance of leakage thus increases with time. If the packing material is not replaced before the leakage becomes dangerous, a disasterous situation could develop.